Molecular Dynamics Simulation of the Structural, Mechanical, and Reprocessing Properties of Vitrimers Based on a Dynamic Covalent Polymer Network

Recyclability and reprocessability of permanently cross-linked polymeric materials have received considerable scientific and technological attention in view of the environmental pollution and sustainable development. By introducing dynamic covalent bonds, vitrimers are emerging as a promising attempt to address this pressing challenge. However, there is still a lack of thermodynamic and kinetic understanding of the bond exchange reactions (BERs) of vitrimers at the molecular level. Herein, by employing coarse-grained molecular dynamics simulations, we successfully construct a model vitrimer system composed of a polymer network formed from linear chains, which can rearrange the network topology via BERs. In this study, we examine the effect of the bond swap energy barrier (ΔE_sw) on a variety of mechanical properties. We find that ΔE_sw critically controls the dynamics of the linear chains and the reactive beads located on the linear chain. Our results indicate that the best mechanical performance characteristics are achieved at an intermediate value of ΔE_sw. Meanwhile, stress relaxations are examined for different ΔE_sw systems. By performing a triaxial deformation to induce the cavities, the vitrimer exhibits excellent self-healing capability by decreasing ΔE_sw, as well as increasing the self-healing time and temperature. Lastly, extrusion of polymer vitrimer is simulated, and we find that the extrusion rate tends to increase linearly as ΔE_sw decreases. In general, our results provide rational guidelines for designing high-performance vitrimers with good mechanical properties, excellent self-healing ability, and good reprocessability.